Relative Velocity of Light and Radio Waves in Space

Book excerpt: Astronomical measurements, because of the great distances involved, hold the promise of extremely precise determinations of the relative velocities of electromagnetic waves from the observation of distant events that occur simultaneously or nearly simultaneously at different wave-lengths. The recent observations of optical and radio events in flare stars now provide the basis for such determinations. Table 1 presents the relevent data now available concerning optical and radio events in four flare stars (column 1). The second and third columns contain the stellar parallax and the corresponding time of light travel. Column 4 gives the interval of time in minutes between the first observation of the optical event and the beginning of the radio event. The photographic observations were made at intervals of 2 min with exposures of several seconds. The successive columns contain the radio frequency of observation. (Author).